1. Field of the Invention
The present invention relates to a thin-film magnetic head structure for manufacturing a thin-film magnetic head which performs perpendicular magnetic recording operations, a method of manufacturing the same, and a thin-film magnetic head.
2. Related Background Art
In recent years, the areal density in hard disk drives has been increasing remarkably. Recently, the areal density in hard disk drives has reached 160 to 200 GB/platter in particular, and is about to increase further. Accordingly, thin-film magnetic heads have been required to improve their performances.
In terms of recording schemes, thin-film magnetic heads can roughly be divided into those for longitudinal recording in which information is recorded in a (longitudinal) direction of a recording surface of a hard disk (recording medium) and those for perpendicular recording in which data is recorded while the direction of recording magnetization formed in the hard disk is perpendicular to the recording surface. As compared with the thin-film magnetic heads for longitudinal recording, the thin-film magnetic heads for perpendicular recording have been considered more hopeful, since they can realize a much higher recording density while their recorded hard disks are less susceptible to thermal fluctuations.
Conventional thin-film magnetic heads for perpendicular recording are disclosed, for example, in U.S. Pat. No. 6,504,675, U.S. Pat. No. 4,656,546, U.S. Pat. No. 4,672,493, and Japanese Patent Application Laid-Open No. 2004-94997.
Meanwhile, when thin-film magnetic heads for perpendicular recording record data onto areas in inner and outer peripheries of a hard disk, a magnetic pole end part disposed on the side of a medium-opposing surface (also referred to as air bearing surface, ABS) opposing the recording medium (hard disk) yields a certain skew angle with respect to a data recording track. In perpendicular magnetic recording heads (hereinafter also referred to as “PMR”) having a high writing capability, the skew angle generated in the magnetic pole end part has caused a problem of so-called side fringe in which unnecessary data are recorded between adjacent tracks. The side fringe adversely affects the detection of servo signals and the S/N ratio of reproduced waveforms. Therefore, in conventional PMRs, the magnetic pole end part on the air bearing surface side in the main magnetic pole layer has a bevel form gradually narrowing in width toward one direction (see, for example, Japanese Patent Application Laid-Open Nos. 2003-242067 and 2003-203311 in this regard).
In a PMR head in which the magnetic pole end part on the air bearing surface side of the above-mentioned main magnetic pole layer is formed like a bevel, the width of the magnetic pole end part (hereinafter referred to as magnetic pole width) is not sufficiently uniform, so that it is uneven in the longitudinal direction of the main magnetic pole layer. Therefore, when the above-mentioned magnetic pole end part of the main magnetic pole layer formed on the wafer is cut at a predetermined position so as to define the air bearing surface of the main magnetic pole layer, it has been problematic in that the magnetic pole width on the air bearing surface may vary depending on the cutting position Therefore, in the conventional PMR, there have been cases where the track width (recording track width) in the air bearing surface greatly varies among products.
Hence, the inventors have proposed a thin-film magnetic head structure equipped with a base insulating layer having a magnetic pole forming depression which has been sunken into a form corresponding to the main magnetic pole layer beforehand and includes a very narrow groove part having a substantially uniform width. This magnetic pole forming depression includes a variable width depression continuously extending from an end part of the very narrow groove part while gradually increasing the width as distanced farther from the very narrow groove part, and a fixed width depression continuously extending from an end part of the variable width depression. When such a base insulating layer is used, the main magnetic pole layer is formed so as to be embedded in the magnetic pole forming depression. Therefore, when the main magnetic pole layer is cut at the very narrow groove part in the magnetic pole forming depression at the time of defining the air bearing surface, the magnetic pole width in the air bearing surface becomes the same width at a high precision.
However, the following problem may occur when forming the above-mentioned magnetic pole forming depression into a base insulating layer.
The above-mentioned magnetic pole forming depression is made by the steps of applying a photoresist onto a base insulating layer made of alumina (Al2O3); patterning the photoresist using a predetermined photomask, so as to form a resist layer exposing the surface of the base insulating layer into a form corresponding to the magnetic pole forming depression; and then performing reactive ion etching (hereinafter referred to as RIE) while using the resist layer as a mask, so as to remove the part not formed with the resist layer. The opening width of the resist layer corresponding to the very narrow groove part is much smaller than the opening width of the resist layer corresponding to the variable depression and fixed width depression. Therefore, when performing RIE using such a resist layer, radical ions substantially vertically enter the portion corresponding to the very narrow groove, but do not have such a directivity so much in the portion corresponding to the variable width depression and fixed width depression and are likely to enter there in directions other than the substantially vertical direction as well. Consequently, in the magnetic pole forming depression formed by RIE, the angle of inclination of side faces has been smaller in the very narrow groove part than in the other parts. Therefore, the decrease in bottom area with respect to the opening area other than the very narrow groove part is much more remarkable than the decrease in bottom area with respect to the opening area of the very narrow groove part, so that the volume of magnetic pole forming depression decreases. Hence, when the main magnetic pole layer is formed by using such a magnetic pole forming depression, the quantity of magnetism (also referred to as magnetic volume) in the main magnetic pole layer decreases, which makes it hard to further improve the overwrite characteristic.